Mercury cathode discharge tube



April 18, 1939. H. LEMS MERCURY CATHODE DISCHARGE TUBE Filed June 26,1957 Patented Apr. 18, 1939 UNITED STATES 2,155,138 IIIERCURY OATHODEDISCHARGE TUBE Hendrik Lems, Eindhoven, Netherlands, assignor to N. V.Philips Glceilampenfabrieken, Eindhoven, Netherlands Application June26,

1937, Serial No. 150,625

In Germany July 28, 1936 6 Claims.

My invention relates to mercury-cathode discharge tubes of the type inwhich a protective metal member is used to prevent the cathode spot frompassing from a cathode-spot anchoring body over the surface of themercury to the tube wall.

Although I shall describe my invention in con nection withmercury-cathode discharge tubes in which the mercury-cathode is disposedwithin a cup-shaped metal envelope portion, it is not limited thereto,but is equally applicable to other types of mercury-cathode tubes.

With such tubes the anchoring body should be maintained at a lowtemperature so that a maximum amount of heat may be withdrawn l 5 fromthe mercury at the anchoring area to thereby increase the stability ofthe cathode focus line. Even if this body is maintained at a lowtemperature and a protective ring is used, the cathode spot may leavethe anchoring body for go some reason or other and pass over theprotective ring to reach the tube wall.

The object of my invention is to make this undesired passage of thecathode spot more difiicult than in the prior art constructions withoutat the same time deleteriously affecting the anchoring power of theanchoring body.

According to the invention, I arrange tire anchoring body in goodheat-transferring relationship with the tube envelope to maintain thisbody at a low temperature, whereas I mount the protective ring in poorheat-transferring relationship with the envelope so that it will bemaintained at a high temperature to prevent the mercury from condensingupon its surface.

In one embodiment of the invention I arrange the protective ring abovethe mercury cathode at such a small distance that the ring retains allits protective properties, but is in poor heat-transferring relationshiptherewith.

In a preferred embodiment, I use an annular anchoring body and arrangethe protective ring above this body and secure it thereto by a poorheat-transmitting connection. In such a construction the protective ringseparates the mer- 1 cury surface within the anchoring body from thesurface of the anchoring body adjacent the tube wall, while at the sametime is in poor heattransmitting relationship with the body and the tubeWall.

In order that the invention may be clearly understood and readilycarried into effect, I shall describe the same in more detail withreference to the accompanying drawing, in which:

Figure 1 is a sectionized view of a mercurycathode rectifier tubeembodying the invention; and

Fig. 2 is a View of a portion of Fig. l drawn to actual size.

The rectifier illustrated in Figure 1 has an en- 7 velope comprising acup-shaped metal member I, for instance of chrome iron, and a glassmember 2 hermetically fused together at IT. Disposed in the bottom ofmember I is a mercury cathode 3, whereas a main anode 8 is supportedfrom 1 the lower end of a conductor 8 Whose upper end is secured to ametal disc 4 hermetically sealed in glass portion 2 carrying a suitableterminal. Supported from conductor 6 and surrounding anode 8 iscylindrical screen I I serving to protect the higher internal surfacesof portion I and seal I? from the detrimental effects of the discharge.

Supported by screen II, which is preferably of sheet molybdenum, is aninsulating tube 26 through the bore of which extends a conductive rod I9carrying on its lower end an auxiliary anode 9. Anode 9 is adapted to bemoved in the direction of the double-headed arrow, and for this purposecarries on its upper end a plunger I8 of magnetic material electricallyconnected through a compression spring 21 to a core 28 of magneticmaterial. Core 28 is supported from the lower end of a conductive rod 'Isecured to a disc 5 hermetically sealed in glass portion 2. Outside theenvelope and surrounding core 28 is coil 5 6 which serves to raise anode9 from the surface of the mercury.

Surrounding cup-shaped member I is a cooling jacket I2 having an inletopening I3 and an outlet opening M, and through which a cooling medium,such as water, is circulated in the direction of the arrows duringoperation of the rectifier. Jacket I2 is secured to member I by a copperbolt I5 secured, for instance by welding, to the bottom of member I andserving tosupply current to cathode 3.

As shown more clearly in Fig. 2, which shows a portion of Fig. 1 inactual size, an annular anchoring body 20, for instance of nickel, isprovided with recesses 22 and is secured in good heattransferringrelationship to the inner surface of the cup-shaped member I. Disposedabove body 2! with an intermediate space 2! of a fraction of amillimeter, for instance 0.2 mm., is a pror annular; however they may beof other closed forms, e. g. a polygon.

The cathode mercury 3 is so arranged in member I as to cover recesses22, whereas the anchoring body 20 extends slightly above its surface.Thus, the mercury which flows down the inner surface of member I ispermitted to flow back to the center of the mercury-cathode withoutaffecting the delimiting of the mercury surface by the anchoring body. Afurther obstacle against passage of the cathode-spot to the tube wall ispresented by the protective ring 23, which does not engage the cathodemercury at all.

This arrangement insures excellent cooling of the anchoring body 20,while at the same time insures that the protective ring 23 will bemaintained at the highest temperature obtainable without a separateheating device. Because of the intermediate space 2| and the fact thatthe protective ring is not immersed in the mercury, there will besubstantially no transfer of heat energy from the ring to the mercuryand thus to the artificially-cooled tube wall.

The functioning of an arrangement such as illustrated in the drawing,may be explained as follows: It is necessary that the protective ring atthe cathode surface have a very high temperature in order that mercuryparticles will not condense thereon and make the interruption of themercury surface by the ring in the direction of the tube wallineffective, whereby the cathodespot might readily pass outwardly on themercury surface thus formed and eventually reach the tube wall. With theconstruction according to the invention, the protective ring ismaintained at a relatively high temperature which eliminates the abovedifficulty.

In prior constructions the ring, similar to the anchoring body, waspartially immersed in the cathode mercury, whereby it was able totransmit a considerable part of its heat to themercury, particularly inthose cases in which the mercury was artificially cooled, for example bya circulating liquid as shown in the drawing. It will be noted that theconstruction illustrated has the advantage that the anchoring body andthe protective ring occupy no more space in a radial direction, thandoes the anchoring body itself. Furthermore, the thermal conditions areexceptionally good because the anchoring body is in direct contact withthe cooled tube wall, whereas the protective ring with its much highertemperature, is connected to the tube only through the anchoring body.Thus, with a correct construction of the poor heat-transmittingconnection between the ring and anchoring member, a maximum temperatureof the protective ring is insured;

Instead of using the construction shown in the drawing, a poorheat-transmitting connection between ring 23 and body 20 can also beestablished by means of comparatively long connecting pieces of metal orinsulating material. I prefer, however, to use the constructionillustrated.

While I have described my invention with reference to specific examplesand applications, I do not wish to be limited thereto, but desire theappended claims to be construed as broadly as permissible in view of theprior art.

What I- claim is:

1. A mercury-cathode discharge tube comprising an envelope an anode, amercury-cathode within said envelope, a cathode-spot anchoring bodyextending from the surface of said mercurycathode and secured to saidenvelope in good heattransferring relationship, and means to preventpassage of the cathode-spot to the tube wall comprising a metalprotective member mounted in poor heat-transferring relationship withsaid mercury cathode, anchoring body, and tube wall.

2. A mercury-cathode discharge tube comprising an envelope having acup-shaped metal portion, an anode, a mercury cathode within saidcup-shaped portion, a cathode-spot anchoring body secured in goodheat-transferring relationship with said cup-shaped portion andextending slightly from the surface of the mercury-cathode, and means toprevent passage of the cathode-spot to the tube wall comprising a metalprotective member in poor heat-transferring relationship with saidmercury-cathode, anchoring body, and tube wall. a

3. A mercury-cathode discharge tube comprising an envelope, an anode, amercury-cathode within said envelope, a cathode-spot anchoring bodysecured in good heat-transferring relationship with said envelope, saidbody extending slightly from the surface of the mercury and surroundinga portion of said surface, means to prevent passage of the cathode-spotto the tube wall comprising a metal protective member disposed above thesurface of the mercury with a small clearance from said body, andsupporting means of low heat conductivity for said member.

4. A mercury-cathode discharge tube comprising an envelope, an anode, amercury-cathode Within said envelope, an annular cathode-spot anchoringbody secured in good heat-transferring relationship with said envelopeand extending slightly from the surface of the mercury, a metalprotective ring disposed above the surface of the mercury andsurrounding the portion of the mercury surface enclosed within saidanchoring body, said protective ring being spaced a small distance fromthe exposed surface of said anchoring body, and means of low heatconductivity supporting said protective ring. 7

5. A mercury-cathode discharge tube comprising an envelope, an anode, amercury-cathode disposed in said envelope, an annular cathodespotanchoring body secured to said envelope in good heat-transferringrelationship and extending slightly above the surface of the mercurycathode, a protective metal ring disposed above .said body with aclearance of a fraction of a millimeter, and means of low heatconductivity supporting said ring from said body.

6. A mercury-cathode discharge tube comprising an envelope having acup-shaped metal portion, an anode, a mercury-cathode within saidportion, an annular cathode-spot anchoring body secured to said portionin good heat-transferring relationship and extending slightly above thesurface of the mercury, a metal protective ring dis.- posed above saidbody with a clearance of the order of a fraction of a millimeter, andmeans of low heat conductivity supporting said ring from said body andcomprising a plurality of interspaced spot-welds.

HENDRIK LEMS.

